Iron deficiency (ID) is present in around half of patients with heart failure, is associated with more advanced symptoms, worse quality of life and poorer outcomes and may be a risk factor for the development and progression of heart failure. However, how ID is defined by blood markers in heart failure remains a debate. Treatment of ID with intravenous iron in those with heart failure improves symptoms and quality of life, but it remains unclear if benefits extend to reducing hospitalisations for heart failure and cardiovascular death. These gaps in research will form the focus of my thesis.

Through a detailed literature review, chapter one provides an overview of ID in heart failure including prevalence, diagnosis, associations with outcomes and effects of iron therapy in each phenotype of heart failure.

Chapters three, four and five present results from retrospective analysis of a large prospective cohort of ambulatory patients with heart failure from the Hull LifeLab. Chapter six reports pooled data from available randomised clinical trials of patients with heart failure and serum iron deficiency assessing the efficacy of intravenous iron to reduce cardiovascular deaths and hospitalisations for heart failure. Chapter seven reports data obtained from the comprehensive Glasgow-wide SafeHaven, comprising primary and secondary care data of patients with and at risk of heart failure within Greater Glasgow and Clyde.

Data from patients with heart failure of different phenotypes enrolled in the Hull LifeLab was analysed to determine how varying definitions of ID affected clinical characteristics, prevalence of ID and associations with mortality. Irrespective of how it is defined, ID is more common in women, in those with anaemia and in those with heart failure with preserved ejection fraction. A low serum iron (≤13μmol/L) and a low transferrin saturation (TSAT) (